U.S. patent number 10,624,135 [Application Number 15/717,535] was granted by the patent office on 2020-04-14 for apparatus and method for controlling slot usage.
This patent grant is currently assigned to ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. The grantee listed for this patent is ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. Invention is credited to Min Ho Cheong, Hyoung Jin Kwon, Jae Seung Lee, Sok Kyu Lee, Jae Woo Park, Hee Jung Yu.
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United States Patent |
10,624,135 |
Kwon , et al. |
April 14, 2020 |
Apparatus and method for controlling slot usage
Abstract
Provided is slot use control apparatus and method, including an
access point (AP) to control a slotted channel access of a station
(STA) in a wireless local area network (WLAN) includes generating a
synchronization (synch) frame including an identification value
indicating an STA allocated to a slot, and broadcasting the
generated synch frame when a channel is in an idle state at a start
point of the slot.
Inventors: |
Kwon; Hyoung Jin (Daejeon,
KR), Lee; Jae Seung (Daejeon, KR), Cheong;
Min Ho (Daejeon, KR), Yu; Hee Jung (Daejeon,
KR), Park; Jae Woo (Daejeon, KR), Lee; Sok
Kyu (Daejeon, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE |
Daejeon |
N/A |
KR |
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Assignee: |
ELECTRONICS AND TELECOMMUNICATIONS
RESEARCH INSTITUTE (Daejeon, KR)
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Family
ID: |
50141598 |
Appl.
No.: |
15/717,535 |
Filed: |
September 27, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180092132 A1 |
Mar 29, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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14412669 |
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9807804 |
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PCT/KR2013/005994 |
Jul 5, 2013 |
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61746070 |
Dec 26, 2012 |
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Foreign Application Priority Data
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Jul 5, 2012 [KR] |
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10-2012-0073208 |
Jul 5, 2013 [KR] |
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10-2013-0078833 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
74/0891 (20130101); H04W 88/12 (20130101); H04W
84/12 (20130101); H04W 74/08 (20130101) |
Current International
Class: |
H04W
74/08 (20090101); H04W 84/12 (20090101); H04W
88/12 (20090101) |
Field of
Search: |
;370/338 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10-2011-0069070 |
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Jun 2011 |
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KR |
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10-2012-0023838 |
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Mar 2012 |
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KR |
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WO 2010/009039 |
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Jan 2010 |
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WO |
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WO 2010/043947 |
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Apr 2010 |
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WO |
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Other References
International Search Report for PCT/KR2013/005994 filed on Jul. 5,
2013. cited by applicant.
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Primary Examiner: Islam; Rownak
Claims
The invention claimed is:
1. A method for controlling channel access by an access point (AP)
in a wireless local area network (WLAN), the method comprising:
transmitting a synchronization frame that includes a receiver
address (RA) field including an identification value indicating a
first station (STA), wherein the synchronization frame is
transmitted if a channel is in an idle state at a time point when
the first STA wakes up, the time point corresponding to a target
wake time (TWT) targeted to the first STA; configuring a response
waiting time; and when a first contention free-End (CF-End) frame
is received during the response waiting time, transmitting a second
CF-End frame, wherein the first CF-End frame is transmitted by the
first STA that has gained access to the channel and has no more
data to transmit, wherein the synchronization frame is
distinguished from a beacon frame, and is transmitted by the AP
between beacon frames to allow the first STA to access the channel,
wherein when a response frame in response to the synchronization
frame is not received during the response waiting time, the AP
transmits a third CF-End frame, and wherein the second and third
CF-End frames are transmitted by the AP to reset a network
allocation vector (NAV) of a STA receiving the second and third
CF-End frames.
2. The method of claim 1, wherein, the AP waits for the response
frame during the response waiting time after transmitting the
synchronization frame.
3. The method of claim 1, wherein the synchronization frame is
transmitted in a form of a null data packet (NDP) which includes a
Short Training Field (STF) field, a Long Training Field (LTF)
field, a Signal (SIG) field without a Data field.
4. The method of claim 1, wherein the RA field of the
synchronization frame comprises information of at least one of a
partial association identifier (AID) or a partial basic service set
identifier (BSSID).
5. The method of claim 1, wherein the synchronization frame is used
for protecting the TWT for the first STA.
6. The method of claim 1, wherein the response frame transmitted by
the first STA is an uplink data frame.
7. The method of claim 6, wherein the synchronization frame further
includes a Duration field.
8. The method of claim 7, wherein a value of the Duration field is
used for transmitting the response frame by the first STA.
9. The method of claim 7, wherein a value of the Duration field is
used for setting a NAV by at least one STA other than the first
STA.
10. An apparatus of an access point (AP) for controlling channel
access in a wireless local area network (WLAN), the apparatus
comprising: a receiver; a transmitter; and a processor, wherein the
processor is configured to: cause the transmitter to transmit a
synchronization frame that includes a receiver address (RA) field
including an identification value indicating a first station (STA),
wherein the synchronization frame is transmitted if a channel is in
an idle state at a time point when the first STA wakes up, the time
point corresponding to a target wake time (TWT) targeted to the
first STA, configure a response waiting time; cause the receiver to
receive a first contention free-End (CF-End) frame during the
response waiting time, and cause the transmitter to transmit a
second contention free-End (CF-End) frame when the first CF-End
frame is received during the response waiting time, wherein the
first CF-End frame is transmitted by the first STA that has gained
access to the channel and has no more data to transmit, wherein the
synchronization frame is distinguished from a beacon frame, and is
transmitted by the AP between beacon frames to allow the first STA
to access the channel, wherein when a response frame in response to
the synchronization frame is not received during the response
waiting time, the AP transmits a third CF-End frame, and wherein
the second and third CF-End frames are transmitted by the AP to
reset a network allocation vector (NAV) of a STA receiving the
second and third CF-End frames.
Description
TECHNICAL FIELD
The present invention relates to an apparatus and method in which
an access point (AP) managing a network controls a slotted channel
access of a station (STA) in a wireless local area network (WLAN)
environment, and an terminal for operating thereof.
BACKGROUND ART
In a wireless local area network (WLAN), an excessive number of
stations (STAs) in a network or a node may increase a probability
of collisions occurring between the STAs. To solve such an issue, a
method of using a slotted channel access may be proposed. In the
method, an access point (AP) may divide a channel access interval
into a slot having a predetermined length, and allocate, to the
slot, a point in time at which the STA accesses the channel. The AP
may notify the STA of a location and an interval of the allocated
slot using a beacon or a broadcast frame and thus, the STA may
perform a data exchange in the allocated slot by listening to the
beacon. Allocating a slot may allow a predetermined STA or a
predetermined STA group exclusive access to a channel. In this
instance, a disallowed STA may not access the channel and thus, a
number of STAs simultaneously accessing the channel may be reduced.
However, when an STA which does not listen to a beacon or a
predetermined STA of a basic service set (BSS) adjacent to an
overlapping basic service set (OBSS) accesses the channel in the
allocated slot, competition may occur with an STA already allocated
to the slot, because in the allocated slot, the STA may access the
channel using a distributed coordination function (DCF) of a
carrier sense multiple access with collision avoidance (CSMA/CA)
scheme, in lieu of a time division multiple access (TDMA) scheme.
In particular, when the allocated slot corresponds to an uplink
(UL) for transmitting data to the AP, a back-off occurring due to a
collision between the STAs may increase in power consumption. To
ensure that the STA allocated based on the DCF accesses the channel
in view of priority, the AP may need to additionally protect the
slot allocated to the STA. The STA may not make a full use of of
the allocated slot being protected with a method of, for example,
acquiring a network allocation vector (NAV) by a request to
send/clear to send (RTS/CTS) exchange, restricting the channel
access using the beacon by the AP, or using a predetermined frame
for the protection. In this instance, another STA may be allowed to
access the channel by releasing the NAV.
DISCLOSURE OF INVENTION
Technical Solutions
According to an aspect of the present invention, there is provided
a slot use control method for an access point (AP) to control a
slotted channel access of a station (STA) in a wireless local area
network (WLAN), the method including generating a synchronization
(synch) frame including an identification value indicating an STA
allocated to a slot, and broadcasting the generated synch frame
when a channel is in an idle state at a start point of the
slot.
According to another aspect of the present invention, there is also
provided a slot use control apparatus for an AP to control a
slotted channel access of an STA in a WLAN, the apparatus including
a generator to generate a synch frame including an identification
value indicating an STA allocated to a slot, and a transmitter to
broadcast the generated synch frame when a channel is in an idle
state at a start point of the slot.
Effect of the Invention
According to an aspect of the present invention, it is possible to
reduce power consumption by preventing an occurrence of a collision
between stations (STAs) and decrease a length of a delay in
transmission caused by waiting.
When the STA does not use a slot, or when the slot has a remaining
time after being used, another STA may be allowed to use the slot.
Thus, an efficiency of an entire network resource may increase.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a diagram illustrating a wireless local area network
(WLAN) environment including an access point (AP) and a plurality
of terminals, for example, stations (STAs) to which an embodiment
of the present invention is applied.
FIGS. 2 and 3 are diagrams illustrating an example of using a
synchronization (synch) frame for avoiding an occurrence of a
collision and saving power when two STAs waking up from a sleeping
state in a conventional slotted channel access scheme are a hidden
node to each other.
FIG. 4 is a flowchart illustrating the slot use control method
according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating an example of using a duration
value in the slot use control method according to an embodiment of
the present invention.
FIGS. 6 and 7 are diagrams illustrating an operation of releasing a
slot in the slot use control method according to an embodiment of
the present invention.
FIG. 8 is a diagram illustrating an operation of supporting a
schedule-negotiated station in the slot use control method
according to an embodiment of the present invention.
FIG. 9 is a diagram illustrating a configuration of the slot use
control apparatus according to an embodiment of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments will be described in detail with reference
to the accompanying drawings.
When it is determined detailed description related to a related
known function or configuration they may make the purpose of the
present invention unnecessarily ambiguous in describing the present
invention, the detailed description will be omitted here. Also,
terminologies used herein are defined to appropriately describe the
exemplary embodiments of the present invention and thus may be
changed depending on a user, the intent of an operator, or a
custom. Accordingly, the terminologies must be defined based on the
following overall description of this specification.
FIG. 1 is a diagram illustrating a wireless local area network
(WLAN) environment including an access point (AP) and a plurality
of terminals, for example, stations (STAs) to which an embodiment
of the present invention is applied.
In a WLAN defined by the Institute of Electrical and Electronics
Engineers (IEEE) 802.11 standard, an environment in which a network
includes an excessive number of STAs or a probability of collisions
occurring between STAs due to a hidden node may be provided. To
solve this issue, a method of applying a slotted channel access
scheme may be used in the environment. In the method, an AP 100 may
divide a channel access interval into a slot having a predetermined
length and allocate, to the slot, a point in time point at which an
STA accesses a channel.
A core principle of the method is to reduce a number of STAs
simultaneously accessing a channel by varying a channel access time
for each STA. To this end, the AP 100 may notify the STA of a
location and an interval of the allocated slot using a beacon or a
broadcast frame so that the STA may listen to the beacon and
perform a data exchange in the allocated slot. In this instance,
since a disallowed STA may not access the channel, the number of
STAs simultaneously accessing the channel may be reduced.
However, when an STA accessing a channel without listening to a
beacon or a predetermined STA of a basic service set (BSS) adjacent
to an overlapping basic service set (OBSS) accesses the channel in
the allocated slot, competition may occur with an STA already
allocated to the slot, because, in the allocated slot, the STA may
access the channel using a distributed coordination function (DCF)
based on a carrier sense multiple access with collision avoidance
(CSMA/CA) scheme, in lieu of using a time division multiple access
(TDMA) scheme. For example, the AP 100 may allocate a predetermined
slot to a station group including an STA-2 120 and an STA-3 130 and
broadcast a location and an interval of the slot allocated to the
station group including the STA-2 120 and the STA-3 130. However,
when an STA-1 110 fails to receive a broadcast frame, the STA-1 110
may try to access the slot allocated to the station group. In this
case, competition may occur, in the corresponding slot, between the
STA-1 110 and the station group including the STA-2 120 and the
STA-3 130.
When the allocated slot corresponds to an uplink (UL) for
transmitting data to the AP 100, a back-off may occur due to a
collision between the STAs, which may lead to power consumption for
reception resulting from channel listening and power consumption
for transmission being greater than the power consumption for
reception. Thus, reducing an occurrence of the collision between
the STAs is required.
Hereinafter, a method of reducing power consumption of the STA
which is allocated using the conventional slotted channel access
scheme will be described with reference to FIGS. 2 and 3.
FIGS. 2 and 3 are diagrams illustrating an example of using a
synchronization (synch) frame for avoiding an occurrence of a
collision and saving power when two STAs waking up from a sleeping
state in a conventional slotted channel access scheme are a hidden
node to each other.
An STA that wakes up at a slot start by receiving an allocated slot
from an AP may be unaware of the existence of the hidden node. To
assist with this, the AP may transmit the synch frame when a
channel is in an idle state at the slot start.
Referring to FIG. 1, in the conventional slotted channel access
scheme, the STA may receive a synch frame 202 from the AP at a slot
boundary 201 and access a channel using a DCF. For example, in 210,
the STA in an awake state may receive a beacon message from the AP.
In 220, the STA may wake up at the slot boundary 201 and wait for a
channel synch. In this instance, the AP may transmit the synch
frame 202 from the slot boundary 201 to the STA. In 230, the STA
may synch to the channel using the synch frame 202 received from
the AP, and start a channel access according to DCF rules.
As another conventional operation example, referring to FIG. 3,
when an AP senses the channel is busy or is in a process of
receiving data from the STA at a slot boundary 301, the AP may not
transmit the synch frame in 302. Since the STA does not receive the
synch frame, the STA may wait without accessing the channel.
According to a waiting rule of an STA, the waiting may be continued
until one of (i) receiving the synch, (ii) receiving another frame
from the access point, and (iii) ending of Probe delay interval is
satisfied.
Accordingly, the STA, which wakes up at the allocated slot boundary
301 and tries to access the channel, may be unaware whether the
corresponding channel is occupied. Thus, the STA may determine
whether the corresponding channel is occupied using the synch frame
transmitted from the AP, and synch to a medium by receiving the
synch frame to access the channel.
For example, in 310, when an STA-x is a hidden node with respect to
an STA-n, the STA-x may be in a process of transmitting a packet to
the AP crossing the slot boundary 301. In 320, the STA may wake up
at the slot boundary 301 and wait for the packet to synch to the
medium. Here, the STA may not listen to a data packet from the
STA-x. In 330, the STA may synch to the channel by receiving an ACK
frame from the AP.
In a conventional method of FIGS. 5 and 6, an operation of an
allocated STA is explained without describing operations of another
STA in a network. The other STA, aside from the allocated STA, may
also wake up and initiate a channel access by receiving a synch
frame. In this instance, an operation of an STA may vary depending
on whether an access of the STA allocated to a slot is to be
allowed or an access of all STAs receiving the synch frame is to be
allowed. Thus, predeterminations with respect to the operation of
the allocated STA and the operation of the other STA in a network
are equally required.
FIG. 4 is a flowchart illustrating the slot use control method
according to an embodiment of the present invention.
Referring to FIG. 4, an AP may control a slotted channel access of
an STA in a WLAN. Hereinafter, a method of controlling the slotted
channel access of an STA by the AP is referred to as the slot use
control method.
In operation 410, a synch frame indicating an STA allocated to a
slot may be generated using the slot use control method. The STA
allocated to a slot may be a single STA or a station group
including a plurality of STAs.
Depending on a case, the synch frame may be generated by setting a
receiver address (RA) value in a media access control (MAC)
header.
In the slot use control method, when a short MAC (SM) header is
used to reduce a scale of the MAC header, a receiver association
identification (AID) value and a basic service set identification
(BSSID) value may be used in lieu of the RA value. For example, the
synch frame may be generated by setting the receiver AID value and
the BSSID value to the SM header. In this instance, since an AID is
unique to a basic service set (BSS), an STA may be uniquely
identified through concurrent use of a BSSID.
When the station group is hierarchically divided using the AID
value, the station group may be identified based on most
significant bits (MSBs) of the AID used to identify a group. For
example, when the STA allocated to a slot corresponds to the
station group including a plurality of STAs and the station group
is hierarchically divided using the AID value, the synch frame may
be generated using a value of MSBs of the AID value as an
identification value in the slot use control method.
Depending on an example, least significant bits (LSBs) may be
allowed to use one pattern. In the slot use control method, a value
of LSBs of the AID value may have identical patterns. For example,
all the LSBs may be set to "0".
However, since the station group may include an STA having a
combination of MSBs and LSBs, a separate bit field may be prepared
to identify a group station and a unique station. In the slot use
control method, when the STA allocated to a slot corresponds to the
group station including a plurality of STAs, the synch frame may be
generated by setting an identification bit field to identify the
group station and the unique station included in the station
group.
Since the synch frame is transmitted to each frame, having a
shorter length of the synch frame may be advantageous. Thus, the
synch frame may be provided in a format of a null data packet
(NDP). The NDP may be a frame including a preamble. The preamble
may include a long training field (LTF), a short training field
(STF), and a signal (SIG) field for synchronization and channel
estimation. Thus, the receiver AID and the BSSID may be applied to
the SIG field. In the slot use control method, the synch frame may
be generated in a format including at least one of the LTF, the
STF, and the SIG field. In the slot use control method, the
receiver AID value and the BSSID value may be set in the SIG field
for setting of the synch frame.
In this instance, a partial AID or a partial BSSID may be used due
to a limitation on a number of bits in the SIG field. Also, a form
of scrambling may be used because a unique determination may not be
performed with the partial AID or the partial BSSID. Thus, the
partial AID value or the partial BSSID value may be set in the SIG
field in the slot use control method.
As described above, when the synch frame including the
identification value is generated and when the channel is in an
idle state at a start point of the slot, the generated synch frame
may be broadcast in operation 420. Thus, when the synch frame is
received, the STA indicated in the synch frame may be allowed a
channel access. Other STAs which are disallowed the channel access
may wait.
Depending on an example, a duration value may be notified for
saving power of other STAs aside from an indicated STA in the slot
use control method. Hereinafter, an example of using the duration
value will be described with reference to FIG. 5.
FIG. 5 is a diagram illustrating an example of using a duration
value in the slot use control method according to an embodiment of
the present invention.
Referring to FIG. 5, in operation 510, an AP 500 may generate a
synch frame to further include the duration value. In the slot use
control method, for example, the synch frame may be generated to
include the duration value and an identification value indicating
an STA 501 allocated to a slot. In operation 520, when the synch
frame is received, the STA 501 indicated in the synch frame may be
allowed a channel access.
In operation 530, other STAs 502, aside from the STA 501 indicated
in the synch frame, may set a network allocation vector (NAV) using
a received duration value. In operation 540, the other STAs 502 may
not access a channel until the NAV corresponds to "0". For example,
the other STAs 502 may be changed into a sleep status until the NAV
corresponds to "0". Thus, the STA 501 allocated to the slot may be
protected from an occurrence of collisions.
As an example, when an NDP is used, a duration field may not be
added due to a limitation on a number of bits. In this example, a
length of an interval may be indicated using a value determined
implicitly. The synch frame may be transmitted in each of the
intervals. In the slot use control method, a value indicating a
length of an interval in which the synch frame is retransmitted may
be set. Also, the synch frame may be retransmitted in each of the
intervals having the predetermined value.
An interval value generally has the same meaning as a meaning of a
slot duration. Since the interval value is used for an STA which
does not listen to a beacon or an STA of an OBSS, the interval
value may be a fixed value rather than a varying value, such as,
the slot duration. For example, the value indicating a length of an
interval in which the synch frame is retransmitted may be set to
the fixed value. Transmitting the synch frame in each of fixed
intervals is to protect a slot from being used by an STA entering a
channel in an allocated slot interval.
According to an example embodiment of the present invention, a slot
being protected may be released so that another STA may be allowed
access. Hereinafter, an operation of releasing a slot will be
described with reference to FIGS. 6 and 7.
FIGS. 6 and 7 are diagrams illustrating an operation of releasing a
slot in the slot use control method according to an embodiment of
the present invention.
Protection of the allocated slot may be implemented using one of
acquiring an NAV by an RTS/CTS exchange, restricting access using a
beacon by an AP, setting the NAV using a synch frame including a
duration field, and the like, or a combination thereof.
An STA allocated to the slot may not make a full use of a slot
being protected. In this instance, a CF-end frame may be used to
allow an access of another STA by releasing an NAV in the slot use
control method according to an embodiment.
Referring to FIG. 6, when an STA 601 allocated to a slot being
protected does not enter, the slot may be released in the slot use
control method.
Referring to FIG. 6 again, in a case of a UL, an AP 600 may
transmit a synch frame in operation 610. Also the AP 600 may wait
for a frame from the STA 601 allocated to the slot to be
received.
In operation 620, when the frame is not received from the STA 601
allocated to the slot during a period of data sensing time 603, the
CF-end frame may be transmitted in the slot use control method. For
example, the AP 600, by transmitting the CF-frame, may notify
another STA 602 aside from the STA 601 allocated to the slot, of
release of the allocated slot
In operation 630, the other STA 602 received the CF-end frame may
reset a predetermined NAV. In operation 640, the other STA 602 may
access a channel. In this instance, the other STA 602 may start the
channel access after recognizing a duration field value included in
the CF-end frame.
In a case of a downlink (DL), the AP 600 may transmit a request
management frame to the STA 601 allocated to the slot in operation
610. In operation 620, when a response management frame in response
to the request management frame is not received from the STA 601
allocated to the slot during a predetermined period of the data
sensing time 603, the AP 600 may be aware that an STA is absent and
transmit the CF-end frame. Here, the response management frame may
be, for example, an ACK frame with respect to data transmitted to
the STA 601 allocated to the slot, a CTS frame pertaining to an
RTA, a response management frame pertaining to a management frame
having a format of a request, and the like. An operation of the
other STA 602 received the CF-frame may be identically performed to
the case of the UL.
Referring to FIG. 7, when data to be subsequently used is absent
during use of a channel, an STA 701 allocated to a slot may release
the channel.
In operation 710, when a frame to be subsequently transmitted is
absent, the STA 701 allocated to a slot may transmit a CF-end frame
to an AP 700. Depending on a case, the STA 701 may set a value
including a sum of a time for transmitting a CF-end frame, a short
interframe space (SIFS), and a time for transmitting a response
CF-end frame as a duration field value.
In operation 720, the AP 700 may receive the CF-end frame from the
STA 701 allocated to the slot and set the duration field value as
"0".
In operation 730, the AP 700 may transmit the CF-end frame to which
the duration field value is set to "0", to the other STA 702 aside
from the STA 701 allocated to the slot.
In operation 740, when the other STA 702 receives at least one of
the CF-frame transmitted from the STA 701 allocated to the slot and
the CF-end frame transmitted from the AP 700, the other STA 702 may
access the channel after a channel duration time ends.
According to an embodiment of the present invention, a method of
NAV setting by using the duration field and a method of
transmitting the synch frame for each predetermined interval during
a data exchange may be applied to a resource allocated by being
scheduled without using a slotted channel access. Hereinafter, a
further description will be provided with respect to FIG. 8.
FIG. 8 is a diagram illustrating an operation of supporting a
schedule-negotiated station in the slot use control method
according to an embodiment of the present invention.
An AP may support an STA that wakes up based on a negotiated
schedule and tries to perform a data exchange. The STA may have a
low-duty cycle, for example, a sensor, and be sensitive to power
consumption. Thus, the STA may perform the data exchange by waking
up at a scheduled time. The AP may notify a predetermined STA of
time information after an allocation is performed. Here, the time
information may include a target wake time (TWT) indicating a time
to wake up, and an interval indicating an allocated time interval
after waking up. Similar to the aforementioned case of the slotted
channel access, when the STA wakes up at the TWT, a collision may
occur due to a hidden node. For example, the collision may occur
when the other STA wakes up while the STA is in a process of
transmitting data, or when an OBSS STA, which is a hidden node with
respect to the STA transmitting data, is present. Since a
significant reduction in power consumption of the STA is required
to avoid an occurrence of the collision, the AP may transmit the
synch frame in a middle of data, and transmit a duration field
including a remaining time for an allocated time interval.
In operation 810, an STA may wake up at a TWT 801 and wait for a
channel synch. In operation 820, to assist the STA to rapidly synch
to a channel, the AP may transmit the synch frame at the TWT 801
when the channel is in an idle state. In operation 830, the STA may
synch to the channel by receiving the synch frame, and start a
channel access according to enhanced distributed channel access
(EDCA) rules. In operation 840, when data transmission ends, the
STA may revert to a sleep mode.
FIG. 9 is a diagram illustrating a configuration of a slot use
control apparatus according to an example embodiment.
Referring to FIG. 9, a slot use control apparatus 900 may control a
slotted channel access of an STA in a WLAN. The slot use control
apparatus 900 may be disposed in an AP to be operated.
The slot use control apparatus 900 includes a generator 910 and a
transmitter 920.
The generator 910 may generate a synch frame including a value
indicating an STA allocated to a slot. The STA allocated to a slot
may be a single STA and a station group including a plurality of
STAs.
Depending on a case, the synch frame may be generated by setting an
RA value in an MAC header.
When an SM header is used to reduce a scale of the MAC header, a
receiver AID value and a BSSID value may be used in lieu of an RA
value. For example, the synch frame may be generated by setting the
receiver AID value and the BSSID value to the SM header in the slot
use control method. In this instance, since an AID is unique to a
BSS, an STA may be uniquely identified through concurrent use of a
BSSID.
When the station group is hierarchically divided using the AID
value, the station group may be identified based on MSBs of the AID
used to identify a group. For example, when the STA allocated to a
slot corresponds to the station group including a plurality of STAs
and the station group is hierarchically divided using the AID
value, the generator 910 may generate the synch frame using a value
of MSBs of the AID value as an identification value.
Depending on an example, LSBs may be allowed to use one pattern. In
terms of the generator 910, a value of LSBs of the AID value may
have identical patterns. For example, the value of LSBs may be set
to "0".
However, since the station group may include an STA having a
combination of MSBs and LSBs, a separate bit field may be prepared
to distinguish a group station and a unique station. When the STA
allocated to a slot corresponds to the group station including a
plurality of STAs, the generator 910 may generate the synch frame
by setting an identification bit field to identify the group
station and the unique STA included in the station group.
Since the synch frame is transmitted to each frame, having a
shorter length of the synch frame may be advantageous. Thus, the
synch frame may be provided in a form of an NDP. Here, the NDP may
be a frame including a preamble. The preamble may include an LTF,
an STF, and an SIG field for synchronization and channel
estimation. Thus, the receiver AID and the BSSID may be applied to
the SIG field. For example, the generator 910 may generate the
synch frame to have a format including at least one of the LTF, the
STF, and the SIG field. The generator 910 may also set the synch
frame by setting the receiver AID value and the BSSID value to the
SIG field.
In this instance, a partial AID or a partial BSSID may be used due
to a limitation on a number of bits in the SIG field. Also, a form
of scrambling may be used because a unique determination may not be
performed with the partial AID or the partial BSSID. Thus, the
generator may set the partial AID value or the partial BSSID value
to the SIG field.
As described above, when the synch frame including the
identification value is generated and the channel is in an idle
state at a start point of the slot, the transmitter 920 may
broadcast the generated synch frame. Thus, when the synch frame is
received, the STA indicated in the synch frame may be allowed a
channel access. Other STAs which are disallowed the channel access
may wait.
Depending on an example, the generator 910 may add a duration value
for saving power of STAs, aside from an indicated STA.
For example, the generator 910 may generate a synch frame to
include the duration value and an identification value indicating
an STA allocated to a slot. When the synch frame is received, the
STA indicated in the synch frame may be allowed a channel
access.
The other STAs, aside from the STA indicated in the synch frame,
may set an NAV using a received duration value. Also, the other
STAs may not access a channel until the NAV corresponds to "0". For
example, the other STAs may be changed into a sleep status until
the NAV corresponds to "0". Thus, the STA allocated to the slot may
be protected from an occurrence of collisions.
As an example, when an NDP is used, a duration field may not be
added due to a limitation on a number of bits. In this example, a
length of an interval may be indicated using a value determined
implicitly. The synch frame may be transmitted in each of the
intervals. The generator 910 may set a value indicating a length of
an interval in which the synch frame is retransmitted. Also, the
generator 910 may retransmit the synch frame for each of the
intervals having the predetermined value.
An interval value generally has the same meaning as a meaning of a
slot duration. Since the interval value is used for an STA which
does not listen to a beacon or an OBSS STA, the interval value may
use a fixed value rather than a varying value, such as, the slot
duration. For example, the generator 910 may set the value
indicating a length of an interval in which the synch frame is
retransmitted, as the fixed value. Transmitting the synch frame in
each of fixed intervals is to protect a slot use from an STA
entering a channel in an allocated slot interval.
According to an embodiment of the present invention, the slot use
control apparatus may release a slot being protected from the
protection so that another STA may be allowed access.
Protection of the allocated slot may be implemented using one of
acquiring an NAV by an RTS/CTS exchange, restricting an access
using a beacon by an AP, setting the NAV using a synch frame
including a duration field, and the like, or a combination
thereof.
An STA allocated to the slot may not make a full use of a slot
being protected. In this instance, the slot use control apparatus
900 according to an example embodiment may use a CF-end frame to
allow an access of the other STAs by releasing the NAV.
In a case of an UL, the transmitter 902 included in the slot use
control apparatus 900 may transmit the synch frame. Also the slot
use control apparatus 900 may wait for receiving a frame from the
STA allocated to the slot.
When the frame is not received from the STA allocated to the slot
during a period of data sensing time, the generator 910 may be
transmit the CF-end. For example, the slot use control apparatus
900, by transmitting the CF-frame, may notify the other STA aside
from the STA allocated to the slot, of release of the allocated
slot
The other STA received the CF-end frame may reset a predetermined
NAV. Also, the other STA may access a channel. In this instance,
the other STA may start the channel access after recognizing a
duration field value included in the CF-end frame.
In a case of a DL, the transmitter 920 may transmit a request
management frame to the STA allocated to the slot. When a response
management frame responding to the request management frame is not
received from the STA allocated to the slot during a predetermined
period of the data sensing time, the slot use control apparatus 900
may be aware that an STA is absent, and transmit the CF-end frame.
Here, the response management frame may be, for example, an ACK
frame with respect data transmitted to the STA allocated to the
slot, a CTS frame with respect to an RTA, a response management
frame with respect to a management frame in a form of request, and
the like. An operation of the other STA received the CF-frame may
be performed identically to the case of the UL.
Depending on an example, when data to be subsequently used is
absent during use of the channel, the STA allocated to a slot may
release the channel.
When a frame to be subsequently transmitted is absent, the STA
allocated to a slot may transmit the CF-end frame to the slot use
control apparatus 900. As an example, the STA may set a value
including a sum of a time for transmitting the CF-end frame, an
SIFS, and a time for transmitting a response CF-end frame as a
duration field value.
The slot use control apparatus 900 may receive the CF-end frame
from the STA allocated to the slot and set the duration field value
as "0".
Also, the transmitter 920 may transmit the CF-end frame to which
the duration field value is set as "0" to the other STA aside from
the STA allocated to the slot.
When the other STA receives at least one of the CF-frame
transmitted from the STA allocated to the slot and the CF-end frame
transmitted from the AP, may access the channel after a channel
duration time ends.
The method according to the above-described embodiments may be
recorded in non-transitory computer-readable media including
program instructions to implement various operations embodied by a
computer. The media may also include, alone or in combination with
the program instructions, data files, data structures, and the
like. Examples of non-transitory computer-readable media include
magnetic media such as hard disks, floppy disks, and magnetic tape;
optical media such as CD ROM discs and DVDs; magneto-optical media
such as optical discs; and hardware devices that are specially
configured to store and perform program instructions, such as
read-only memory (ROM), random access memory (RAM), flash memory,
and the like. Examples of program instructions include both machine
code, such as produced by a compiler, and files containing higher
level code that may be executed by the computer using an
interpreter. The described hardware devices may be configured to
act as one or more software modules in order to perform the
operations of the above-described embodiments, or vice versa.
Although a few embodiments of the present invention have been shown
and described, the present invention is not limited to the
described embodiments. Instead, it would be appreciated by those
skilled in the art that changes may be made to these embodiments
without departing from the principles and spirit of the invention,
the scope of which is defined by the claims and their
equivalents.
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